The present invention generally relates to fracturing operations, and, more specifically, to sealing existing fractures in a completed wellbore, followed by initiating new fractures therein.
Fracturing operations are often conducted in order to increase production from a subterranean formation. During the course of production from a subterranean operation, it can sometimes become necessary to perform subsequent fracturing operations on the subterranean formation, for example, if the initial fracturing operation failed to introduce sufficient fractures needed to achieve a desired level of production. These subsequent fracturing operations can become much more of a technical challenge due to the presence of the existing fractures in the wellbore. In order to prevent fluid leak off into the subterranean formation during subsequent fracturing operations, it can be necessary to seal the existing fractures in the subterranean formation. Typically, the sealing of existing fractures in the subterranean formation can be conducted with a particulate slurry that deposits a particulate seal within the fractures. The particulate seal can be formulated to degrade at a later time, if desired.
Excess particulate slurry is typically introduced into the subterranean formation, since it can be difficult to precisely determine the volume needed to seal the existing fractures. The presence of the excess particulate slurry in the subterranean formation can inhibit the ability to perform subsequent fracturing operations. Specifically, the presence of a particulate slurry in the subterranean formation can result in a lack of pressure communication from the fluid to the surface of the subterranean formation. That is, the presence of particulates in a subterranean formation can prevent fracturing from occurring, even when a fracturing fluid is introduced into the subterranean formation at a pressure that is typically sufficient to create or enhance at least one fracture therein.
When performing subsequent fracturing operations in a subterranean formation, the particulates used for sealing the existing fractures can sometimes simply be flushed from the subterranean formation prior to fracturing. Although there is no reliable way to conclusively determine that the fluid within the formation is substantially particulate free and suitable for conducting a subsequent fracturing operation, this approach can typically be sufficient for uncompleted wellbores, since adequate fluid circulation can typically be achieved to remove the particulates from the subterranean formation. However, flushing can considerably add to the time and expense of production from the subterranean formation.
For completed wellbores, the issue of eliminating particulates from the subterranean formation can become considerably more problematic. In the case of completed wellbores, where the existing fractures are behind a fracturing sleeve or like barrier, it can be difficult to generate adequate fluid circulation, even with large flushing volumes, to effectively flush the particulates from the wellbore space. The failure to completely remove residual particulates from the wellbore can cause subsequent fracturing operations to fail.